The influence of human growth hormone (HGH) on physiologic processes and exercise

Introduction

Human growth hormone (HGH), also known as somatotropin, is peptide hormone secreted by the anterior pituitary gland Hoffman, J.R., Kraemer, W. J., Bhasin, S., Storer, T., Ratamess, N. A., Haff, G. G., Willoughby, D. S. Rogol, A. D. (2009). Position stand on androgen and human growth hormone use. Journal of Strength and Conditioning Research, 23(5), S1-S59. Doi: 10. 1519/JSC. 0b013e31819df2e6. HGH is an anabolic hormone that builds and repairs tissue, such as collagen and muscle tissue, throughout the bodyHoffman, J.R., Kraemer, W. J., Bhasin, S., Storer, T., Ratamess, N. A., Haff, G. G., Willoughby, D. S. & Rogol, A. D. (2009). Position stand on androgen and human growth hormone use. Journal of Strength and Conditioning Research, 23(5), S1-S59. Doi: 10. 1519/JSC. 0b013e31819df2e6. HGH release is stimulated from the release of growth hormone releasing hormone (GHRH), which is released as a result of exerciseKraemer, W. J., Dunn-Lewis, C., Comstock, B. A., Thomas, G. A., Clark, J. E., & Nindl, B. C. (2010). Growth hormone, exercise, and athletic performance: A continued evolution of complexity. Current Sports Medicine Reports, 9(4), 242. doi:10.1249/JSR.0b013e3181e976df. HGH promotes the release of IGF-1, which promotes anabolic effects within the bodyKraemer, W. J., Dunn-Lewis, C., Comstock, B. A., Thomas, G. A., Clark, J. E. & Nindl, B. C. (2010). Growth hormone, exercise, and athletic performance: A continued evolution of complexity. Current Sports Medicine Reports, 9(4), 242-252. Doi: 10. 1249/JSR. 0b013e3181e976df . HGH is an important component of metabolism by increasing lean body mass and promoting lipolysis Hoffman, J.R., Kraemer, W. J., Bhasin, S., Storer, T., Ratamess, N. A., Haff, G. G., Willoughby, D. S. & Rogol, A. D. (2009). Position stand on androgen and human growth hormone use. Journal of Strength and Conditioning Research, 23(5), S1-S59. Doi: 10. 1519/JSC. 0b013e31819df2e6.Growth Hormone also increases synthesis of muscle protein via amino acid transport and amino acid availibility. It also helps facilitate body's response to exercise, however it's effects are not restricted to protein alone.Kraemer, W. J., Dunn-Lewis, C., Comstock, B. A., Thomas, G. A., Clark, J. E., & Nindl, B. C. (2010). Growth hormone, exercise, and athletic performance: A continued evolution of complexity. Current Sports Medicine Reports, 9(4), 242. doi:10.1249/JSR.0b013e3181e976df HGH is only released periodically, such as during certain stages of sleep, certain parts of the day, and with exercise Kraemer, W. J., Dunn-Lewis, C., Comstock, B. A., Thomas, G. A., Clark, J. E. & Nindl, B. C. (2010). Growth hormone, exercise, and athletic performance: A continued evolution of complexity. Current Sports Medicine Reports, 9(4), 242-252. Doi: 10. 1249/JSR. 0b013e3181e976df.It has been shown that the menstrual cycle and oral contraceptive use have a significant impact on growth hormone levels Sunderland, C., Tunaley, V., Horner, F., Harmer, D., Stokes, K. A. (2011). Menstrual cycle and oral contraceptives’ effects on growth hormone response to sprinting. Journal of Applied Physiology, Nutrition, and Metabolism, 36(4), 495-502.. The periodic release of HGH combined with its positive anabolic and metabolic effects on the body has lead to supplementation of HGH to improve exercise performance.

Musculoskeletal

Athletes

HGH injections and supplements are widely abused by athletes to enhance performance. Nevertheless, there is not enough definititive evidence that HGH improves performanceSaugy, M., Robinson, N., Saudan, C., Baume, N., Avois, L., Mahgin, P. (2006). Human growth hormone doping in sport. British Journal of Sports Medicine, 40, 135-139.One study investigated the impact growth hormones have on body composition and measurable performance in recreational athletesMeinhardt, U., Nelson, A. E., Hansen, J. L., Birzniece, V., Clifford, D., Leung, K., . . . Ho, K. K. fckLR(2010). The effects of growth hormone on body composition and performance in recreational athletes. Annals of Internal Medicine, 152, 568-577.. The authors argued that growth hormone injections increase athletic exercise performance when given alone or with testosterone. In addition, participants that received growth hormones retained more body fluid and frequent joint pain than control group.

Older Adults

HGH injections are not only used for athletes, but for the older population as well. One study analyzed the impact of recombinant human growth hormones and testosterone injections on aerobic and anaerobic fitness, body mass, and lipid profile in adult men Zajac, A., Wilk, M., Socha, T., Maszczyk, A., and Chycki, J. (2014). Effects of growth hormone and fckLRtestosterone therapy on aerobic and anaerobic fitness, body composition and lipoprotein profile in middle-aged men. Annal of Agricultural and Environmental Medicine, 21(1), 156-160.. The data demonstrates that recombinant human growth hormones and testosterone injections significantly increased aerobic and anaerobic capacity, led to changes in body compositions, and decreased total body fat and increased free-fat muscle. In another study, the authors analyzed whether treatment with testosterone and recombinant human growth hormones would increase muscle strength and mass in older adult patientsSchroeder, E. T., He, J., Yarasheski, K. E., Binder, E. F., Castaneda-Sceppa, C., Bhasin, S., . . . Sattler, F. R. (2011). Value of measuring muscle performance to assess changes in lean mass with testosterone and growth hormone supplementation. Europe Journal of Applied Physiology, 112, 1123-1131.. The authors found that recombinant human growth hormones are connected with fluid preservation and improvements in muscle mass and strength that would translate into better aerobic exercise performance.  

Exercise Prescription

Although HGH injections are one of the most common forms of HGH found in the body, the body can naturally produce HGH through certain exercise. An article by Maresh et. al compared two different exercise routines between men and women in order to determine which exercise caused the greatest change in the amount of serum glucose and blood lactate levels within the body as a direct result of the different exercises. This study found that a heavy resistance exercise protocol (HREP) of high volume, 10RM load, and shorter rest periods produced a drastic stimulus of serum hGH levels within the body, while a lower volume and a longer rest period produced and clearer and more sustained elevaton of hGH levels Maresh, C., & Fry, A. C. (1991). Endogenous anabolic hormonal and growth factor responses to heavy resistance exercise in males and females. Int. J. SportsMed, 12, 228-235.. Knowing this, physical therapists should consider volume, repetitions, and rest periods when prescribing exercise for various patients based off the goals set forth between the therapist and the patient.